A gauge holder for mounting strain gauges on a pipe is disclosed in Patent Document 1 for example. The gauge holder includes a sensor mounting bracket which has already been mounted on a sensor, and a mounting bracket having a mounting belt fixed to the pipe so that the sensor mounting bracket straightly abuts against a surface of the pipe. The mounting bracket is configured such that when a shoulder bolt provided on the sensor mounting bracket is threadedly inserted into a mounting boss provided on the mounting belt, a shoulder of the shoulder bolt abuts against the mounting boss and stops at the boss, and thus a sensor is pressed against an object-to-be-measured under constant pressure. This gauge holder mounts the strain gauge on the pipe under constant pressure without using a torque wrench or the like.
Patent Document 2 discloses a gauge holder including an attachment having two arms which can open and close through a hinge, and fastening means provided on opened and closed ends of the arms and fastening the arms in their closing direction. According to this gauge holder, when the two arms are fastened, sensors mounted on the arms are pressed against a pipe.
Patent Document 3 discloses a gauge holder of a structure in which a U-shaped clamp is mounted on a side surface of a pipe through a fixing screw. This gauge holder includes a sensor at a location where a bottom of the clamp and the side surface of the pipe come into contact with each other.
Patent Document 4 discloses a side surface attaching pressure detecting device which includes two half link-shaped flanges, and the flanges include recesses filled with elastic materials. According to this detecting device, the elastic materials press the sensor against a side surface of the pipe with sufficient force.
Further, Non-Patent Document 1 discloses a sandwich type gauge holder which sandwiches a pipe and a gauge holder which is fixed to a pipe by means of a magnet.
However, the gauge holder disclosed in Patent Document 1 has such a structure that the sensor placed in an axial direction of the pipe is fixed to the mounting belt through the shoulder bolts which are placed at upper and lower locations thereof. Therefore, regions which cannot be measured (regions hidden by the mounting belt) exist at the upper and lower locations of the sensor. Hence, there is a problem that strains cannot be measured in the vicinity of a pipe-welded portion where the pipe is connected by welding and in the vicinity of a bent angle of a bent pipe.
Furthermore, the gauge holder disclosed in Patent Document 1 has a structure using the mounting bracket on which the strain gauge is mounted in advance. Therefore, it is necessary to respectively prepare mounting brackets on which strain gauges suitable for measurement purposes, such as strain gauges for multiaxial measurement, strain gauges for shearing strains and strain gauges for high temperature are mounted. Hence, any commercially available foil strain gauge cannot be mounted as they are, and there is also a problem that general versatility is poor.
Furthermore, when a diameter of the pipe and a diameter of the mounting belt do not match with each other, since the mounting belt is distorted, there is also a problem that strains at the precise two points existing on a diameter of the pipe cannot be measured. Further, in order to secure constant pressing pressure by the shoulder bolt, it is necessary to enhance rigidity of the mounting belt so that the mounting belt does not become deformed. On the other hand, in order to attach the mounting belt to the pipe without plastically deforming the mounting belt, it is necessary to lower the rigidity of the mounting belt. In order to satisfy these two conditions, the mounting belt includes a cut-out at a position forming an angle of about 90° with respect to the mounting bracket. Therefore, the strain gauges cannot be placed at these areas, and there is also a problem that strains cannot be measured at two points forming 90° on the same plane.
The gauge holder disclosed in Patent Document 2 is mounted on a pipe by fastening the arms. Hence, the sensor can be placed even in the vicinity of the pipe-welded portion and in the vicinity of the bent angle of the bent pipe. However, since strains can be measured only at the two points on the diameter of the pipe, there is a problem that strains cannot be measured at two points forming 90° on the same plane.
Furthermore, the gauge holder disclosed in Patent Document 2 has a structure in which the sensor is mounted in a groove provided in the arms. Therefore, it is necessary to prepare in advance a sensor which is suitable for the groove. Hence, any commercially available foil strain gauges cannot be mounted as they are, and there is also a problem that general versatility is poor.
According to the gauge holder disclosed in Patent Document 3, forces pressing the strain gauges act only in an inserting direction of the bolt. Hence, positions where the strain gauges can equally be pressed are only two points located at 90° in a circumferential direction from the bolt, i.e., only two points on the diameter. Therefore, there is a problem that strains cannot be measured at two points forming 90° on the same plane.
Furthermore, the gauge holder disclosed in Patent Document 3 has a configuration of using a sensor in which strain gauges are mounted in advance on a cylindrical fixing member. Hence, any commercially available foil strain gauges cannot be mounted as they are, and in order to use strain gauges desired by a user, time and labor for machining a holder are needed.
The gauge holder disclosed in Patent Document 4 has a structure in which two half ring-shaped brackets are tied on the pipe and mounted thereto through a bolt, and the elastic materials filling the recesses formed inside of a ring press the sensor against the pipe. According to this holder, like the holder of Patent Document 3, a force pressing the strain gauge acts only in an inserting direction of the bolt. Hence, positions where the sensor can equally be pressed are only two points located at 90° in a circumferential direction from the bolt, i.e., only two points on the diameter. Therefore, there is a problem that strains cannot be measured at two points forming 90° on the same plane.
The sandwich type gauge holder disclosed in Non-Patent Document 1 has a problem that the device is large in size, it is difficult to attach the device, and strains cannot be measured at two points forming 90° on the same plane. The magnet type gauge holder disclosed in Non-Patent Document 1 also has a problem that when a plurality of gauges is mounted on the same plane, it is difficult to secure the same pressing pressure.
Further, any of the gauge holders disclosed in Non-Patent Document 1 is a gauge holder for a frictional strain gauge in which a strain gauge is formed on a rigid substrate. Therefore, these gauge holders cannot be applied to a so-called foil strain gauge such as a strain gauge for multiaxial measurement, a strain gauge for a shearing strain and a strain gauge for high temperature.